streamline

streamline, path of a fluid flowing steadily and without appreciable turbulence. A body is said to be streamlined if its shape offers the least possible resistance to a current of air, water, or other fluid. The current that a streamlined body breaks simply reunites in its wake, as contrasted with the retarding eddies and turbulence created by the partial vacuum in the wake of a nonstreamlined body. The streamline design is typically a long ellipse tapering to a point in the direction of flow; it is illustrated in the cross section of an airplane wing and in the bodies of fishes and birds. Vehicles such as automobiles, aircraft, railroad cars, and boats are designed to provide maximum streamline.